The present invention relates to an ink jet print head in which ink droplets are produced corresponding to a print signal. More particularly, the invention relates to ink jet print head of a type having nozzle openings facing upward.
In an on-demand type ink jet print head, piezoelectric elements are operated in response to a print signal to eject ink in the form of ink droplets from nozzle openings onto a recording sheet. The operating cost of such a print head is lower than a conventional print head of the type in which continuously sprayed ink is attracted to a recording sheet by an electrostatic force, and its size is smaller. Thus, the on-demand type ink jet print head is widely used as a print head for small-sized printers.
In an on-demand type ink jet print head, nozzle openings can be arranged horizontally, facing downward or facing upward. The structure in which the nozzle openings are arranged facing upward, wherein printing is performed on a recording sheet that is set above the nozzle openings, allows the print head to recover ink leaked from the print head itself, thereby contributing to easy maintenance.
Such an on-demand type ink jet print head in which the ink ejection nozzles are arranged facing upward is disclosed in Japanese Utility Model Unexamined Publication No. 102539/1987. In the ink jet print head disclosed in this publication, one of the walls of a chamber communicating with the vertically arranged nozzles is formed of a resilient plate, and piezoelectric elements are firmly fixed to the plate. According to this print head, the ink is ejected upward from the nozzles by causing the resilient plate to deform upon application of a print signal to the piezoelectric elements. On the other hand, such deformation of the chamber causes the volume of the ejected ink droplets to be large, thereby disadvantageously entailing a relatively long period of time in drying the recording sheet.
To reduce the volume of the ink droplets, a print head has been proposed in which cantilever-type vibrating plates are arranged in the ink supply confronting the nozzle openings and the ink is jetted from the nozzle Openings by elastic vibration of the vibrating plates. Such a print head is disclosed in Japanese Patent Examined Publication No. 8953/1980. With this print head, the volume of the ink droplets can be made smaller by reducing the size of the vibrating plate.
However, in the print head disclosed in the above Publication No. 8953/1980, it is required that ink be supplied between the nozzle openings and the vibrating plates at all times. Therefore, if the nozzle openings are arranged facing upward in this type of print head, it is extremely difficult to supply the ink between nozzle plate and the vibrating plates.
That is, to introduce the ink between the nozzle plate and the vibrating plates in such a manner that the ink does not leak from the nozzle openings, the ink must be at a higher level than the nozzle plate. However, because it is difficult to supply ink to this region continuously, the size of a reserve tank must be made large to prevent an unwanted decrease in the ink level.